According to the results of a study published in the Journal of Clinical Oncology a bone scan index (BSI) can assess response to treatment and predict survival in metastatic hormone-refractory prostate cancer.

Men who have castrate resistant or metastatic hormone-refractory prostate cancer that no longer responds to hormonal therapy and has spread to distant sites in the body often have bone scans during the course of their treatment. Since bone scans image the bone rather than the cancer and there is no standard measurement of post-treatment changes in the bones or the treatment effects on the cancer.

The bone scan index (BSI) was developed as a quantitative tool to improve interpretability and clinical relevance of the bone scan. The BSI is a method of expressing the tumor burden in bone as a percentage of the total skeletal mass based on a reference man. The reference man provides a standard set of biologic characteristics modeled on a hypothetical young Caucasian male.

Researchers in this study retrospectively examined serial bone scans from 88 men with metastatic hormone-refractory prostate cancer who were enrolled in four clinical trials. They calculated BSI at baseline and at 3 and 6 months on treatment. They found that the percent change in BSI from baseline to 3 and 6 months was predictive for survival. A doubling in BSI was associated with a 1.9-fold increased risk of death.
Additionally, the researchers also compared the BSI with prostate-specific antigen (PSA) levels. They found that a change in PSA was not prognostic for survival.

The researchers found that the BSI provides a quantitative measure—as a single number—of the amount of disease progression or regression as a result of treatment. They concluded that the BSI can prognosticate for survival and is a more accurate indicator of treatment response than PSA. Of course BSI will only work for men with metastasis in their bones, not in soft tissue.

Reference:
Dennis ER, Jia X, Mezheritskiy IS, et al: Bone scan index: A quantitative treatment response biomarker for castration-resistant metastatic prostate cancer. Journal of Clinical Oncology. 2012; 30(5): 519-524.

Joel T Nowak, M.A., M.S.W.